1. Field of the Invention
The present invention relates to a distribution control system for identifying and isolating a fault section when a fault takes place on a distribution line.
2. Description of Related Art
FIG. 7 is a diagram showing a distribution system. In FIG. 7, reference symbols AS/S, BS/S, CS/S, DS/S and ES/S each designate a distribution substation; F1-F9 each designate a distribution line led out of the distribution substation AS/S; F10-F18 each designate a distribution line led out of the distribution substation BS/S; F19-F26 each designate a distribution line led out of the distribution substation CS/S; F27-F34 each designate a distribution line led out of the distribution substation DS/S; F35-F43 each designate a distribution line led out of the distribution substation ES/S; and LS1-LS18 each designate a tie switch for coupling two distribution lines. Although not shown in FIG. 7, a plurality of load break switches are interposed in each distribution line.
FIG. 8 is a block diagram showing a conventional distribution control system, in which the reference numeral 1 designates a distribution transformer of the distribution substation AS/S; 2 designates a secondary main breaker of the distribution transformer 1; and 3 designates a secondary main bus of the distribution transformer 1, from which the distribution lines F1 and F2 are drawn out.
Reference numerals 4 and 5 each designate a distribution feeder breaker; 6-11 each designate a no-voltage opened mode load break switch connecting in series two respective sections of the distribution lines F1 and F2, distribution line F1 including sections F1-1, F1-2, F1-3, and F1-4 and distribution line F2 including sections F2-1, F2-2, F2-3, and F2-4; 12 designates a tie switch for coupling the distribution lines F1 and F2; 13-19 each designate a feeder terminal unit for monitoring a fault current or the like passing through one of the load break switches 6-11 and tie switch 12, for notifying a substation remote terminal unit 20 of presence/absence information about the fault current, and for turning on and off the load break switches 6-11 and tie switch 12 in response to a control signal fed from the substation remote terminal unit 20; and 20 designates the substation remote terminal unit for transferring to a control center 21 the presence/absence information about the fault current supplied from the feeder terminal units 13-19, and for transferring to the feeder terminal units 13-19 the control signal supplied from the control center 21.
The reference numeral 21 designates the control center for managing the distribution of the distribution substation AS/S; 22 designates an information collecting unit for carrying out transmission and reception of information; 23 designates a computer system for identifying a fault section from the presence/absence information supplied thereto, and for producing the control signal commanding to open the load break switches at both ends of the fault section; and A1-A5, B1-B3 and C each designate a communication line.
FIG. 9 is a block diagram showing an internal arrangement of each of the load break switches 6-11 and feeder terminal units 13-18. In FIG. 9, the reference numeral 31 designates a contact maker; 32 designates an operation rod for making or breaking the contact maker 31; 33 designate an actuator of each of the load break switches 6-11; 34 designates a current transformer for detecting a current flowing through the distribution line on the power supply side; 35 designates a control transformer for detecting a voltage on the distribution line on the power supply side; and 36 designates a control transformer for detecting a voltage on the distribution line on the load side.
The reference numeral 37 designates a voltage/phase angle detector connected to the control transformers 35 and 36 for detecting the voltage and phase on the distribution line; 38 designates a current detector connected to the current transformer 34 for detecting the current passing through each of the load break switches 6-11; 39 designates a controller for monitoring an operation state of the switch actuator 33 and the current passing through each of the load break switches 6-11, and for controlling the switch actuator 33 in response to the control signal fed from the substation remote terminal unit 20; 40 designates a communication circuit for exchanging with the substation remote terminal unit 20 various information (such as values detected by the voltage/phase angle detector 37 and current detector 38); 41 designates a battery for supplying power to component circuits of each of the feeder terminal units 13-18 in case of outage of the distribution line; and 42 designates a branch box for connecting the communication circuit 40 of each of the feeder terminal units 13-18 to a communication line.
Next, the operation of the conventional system will be described.
When controlling the distribution system of the distribution substation AS/S, the substation remote terminal unit 20 regularly transmits to the feeder terminal units 13-19 an information transmission request through the communication lines A4 and A5 so as to collect information about the load break switches 6-11 and tie switch 12 (including the presence/absence information of the fault current passing through the load break switches 6-11).
On the other hand, the feeder terminal units 13-19 always collect information about the load break switches 6-11 and tie switch 12, and send the information back to the substation remote terminal unit 20 through the communication lines A4 and A5 in response to the information transmission request sent from the substation remote terminal unit 20.
The information about the load break switches 6-11 and tie switch 12 thus collected by the substation remote terminal unit 20 is transferred to the control center 21. Thus, the information collecting unit 22 in the control center 21 receives the information, and the computer system 23 in the control center 21 identifies the fault section from the information about the load break switches 6-11 and tie switch 12 if a distribution line fault takes place.
Identifying the fault section, the computer system 23 in the control center 21 supplies the substation remote terminal unit 20 with a control signal that commands it to open the load break switches at both ends of the fault section. In response to the control signal, the substation remote terminal unit 20 transfers, to the feeder terminal units managing the load break switches at both ends of the fault section, the control signal commanding to open the load break switches. Thus, the feeder terminal units open the load break switches.
An example will now be described assuming that a distribution line fault takes place in the section F1-3 of the distribution line F1 as shown in FIG. 8.
If a distribution line fault takes place in the section F1-3 of the distribution line F1, a protective relay not shown in FIG. 8 but included in the feeder breaker 4 operates so that the feeder breaker 4 trips and the distribution line F1 is shut down. However, since the load break switches 6-8 are a no-voltage opened mode switch, they open immediately when the distribution line F1 is shut down to a no-voltage state by the distribution line fault.
Counting about 60 seconds after breaking the distribution line F1, the feeder breaker 4 automatically closes again by the operation of an embedded reclosing relay. Accordingly, the power is supplied to the section F1-1, that is, to the power supply side of the load break switch 6. After elapsing about seven seconds, the load break switch 6 automatically closes again so that the power is supplied to the section F1-2, that is, to the power supply side of the load break switch 7. Likewise, after elapsing about seven seconds, the load break switch 7 automatically closes so that the power is supplied to the section F1-3.
If the fault taking place in the section F1-3 is a transitory failure, the section F1-3 will have already been recovered when the load break switch 7 automatically closes. Thus, the distribution line F1 is recovered from the fault. Such a method that sequentially closes the load break switches when a distribution line fault occurs is referred to as a time limited sequential shift method.
On the other hand, if the fault taking place in the section F1-3 is a continuous failure, it will reoccur when the load break switch 7 automatically closes. Thus, the feeder breaker 4 trips again, and the load break switches 6 and 7 open automatically. In response to the fault immediately after the automatic closing, the load break switch 7 considers the section F1-3, one of the load side sections of the load break switch 7, as a fault section, and enters a closing lock mode.
Then, the feeder breaker 4 closes once again after the reoccurrence of the fault so that the power is sequentially applied to the sections F1-1 and F1-2. In this case, since the load break switch 7 is not closed because of the closing lock mode, the time limited sequential shift is completed when it reaches the section F1-2.
Then, the computer system 23 in the control center 21, receiving the information about the load break switches 6-8 from the feeder terminal units 13-15 through the substation remote terminal unit 20, recognizes that because the loadbreak switch 6 is in the close state and the load break switches 7 and 8 are in the open state, the section F1-3 between the load break switches 7 and 8 in the open state is a fault section.
Identifying the fault section in this way, the computer system 23 supplies the substation remote terminal unit 20 with the control signal commanding to open the load break switches 7 and 8. Receiving the control signal, the substation remote terminal unit 20 transfers the control signal to the feeder terminal units 14 and 15 to open the load break switches 7 and 8 at both ends of the fault section F1-3, thereby isolating the fault section.
After isolating the fault section F1-3, the computer system 23 supplies the substation remote terminal unit 20 with the control signal commanding to turn on the tie switch 12 to recover the outage of the health section (the section F1-4 in this case). Receiving the control signal, the substation remote terminal unit 20 transfers the control signal to the feeder terminal unit 19 which closes the tie switch 12. Thus, the health section F1-4 is recovered from the outage.
With the foregoing configuration, the conventional distribution control system can positively isolate the fault section from the health sections using the time limited sequential shift method. However, when the distribution line equipment such as the load break switches 6-11 cannot handle the time limited sequential shift method, a problem arises in that it is necessary to install into the distribution line equipment a device for detecting a fault section.
The present invention is implemented to solve the foregoing problem. It is, therefore, an object of the present invention to provide a distribution control system capable of identifying and isolating a fault section, without employing the time limited sequential shift method and without adding any new devices, by storing in feeder terminal units current values passing through the load break switches when a fault occurs, and by using the fault current values that are stored.
According to one aspect of the invention, a distribution control system for controlling switches, each switch connecting sections of at least one distribution line to a breaker, the distribution control system includes switch controllers, each of the switch controllers controlling an open/close state of one of the switches, and storing, when making a decision that a current passing through the corresponding switch is a fault current, a value of the current as a fault current value; and fault section identifying means for identifying a fault section from the fault current value stored in the switch controllers and generating a clear command to clear a fault current value stored in the switch controllers, wherein each of the switch controllers clears the fault current value stored in response to the clear command.
According to another aspect of the invention, a distribution control system for controlling switches, each switch connecting sections of at least one distribution line to a breaker, the distribution control system includes switch controllers, each of the switch controllers controlling an open/close state of one of the switches, and storing, when making a decision that a current passing through the corresponding switch is a fault current, a value of the current as a fault current value; and fault section identifying means for identifying a fault section from the fault current value stored in the switch controllers, each of the switch controllers clearing the fault current value after a time period elapses following storing of the fault current value.
According to a third aspect of the invention, a distribution control system for controlling switches, each switch connecting sections of at least one distribution line to a breaker, the distribution control system includes switch controllers, each of the switch controllers controlling an open/close state of one of the switches, and storing, when making a decision that a current passing through the corresponding switch is a fault current, a value of the current as a fault current value; and fault section identifying means for identifying a fault section from the fault current value stored in the switch controllers and for identifying, when the breaker trips, the fault section only from fault current values stored in the switch controllers associated with the switches in the distribution line connected to the breaker.